1. Field of the Invention
The present invention relates to a dual damascene process and, more particularly, to a dual damascene process using a single photo mask.
2. Description of the Related Art
Metallic damascene processes are generally divided to single damascene processes and dual damascene processes. FIG. 1a to FIG. 1c illustrate the dual damascene process in the prior art.
In FIG. 1a, substrate 10 maybe a metal layer or a semiconductor layer. A dielectric layer 12, for example, a silicon dioxide layer, is formed on the surface of the substrate 10 by PECVD, and a first photoresist pattern 14 is formed on the surface of the dielectric layer 12 by a first photolithography process. Then, part of the dielectric layer 12 is removed and a first opening 16 is formed by using the first photoresist pattern 14 as the etching mask.
Then, as shown in FIG. 1b, after the first photoresist pattern 14 is removed, a second photolithography process is applied to form a second photoresist pattern 18 on the dielectric layer 12. Then, part of the dielectric layer 12 in the first opening 16 is removed and a second opening 20 is formed in the first opening 16 by using the second photoresist pattern 18 as the etching mask.
Finally, as shown is FIG. 1c after the second photoresist pattern 18 is removed, a metal layer 22 is filled in the first opening 16 and the second opening 20, thus completing dual damascene process.
According to the above description, photolithography must be applied twice during the dual damascene process. Thus two photo masks (or reticles) must be used: the first photo mask used to define the first opening 16 and the second photo mask used to define the second opening 20. However, if the photolithography process using the second photo mask is misaligned, overlay may occur on the first opening 16 and the second opening 20, thus destroying the profile of the dual damascene structure, as shown in FIG. 2.
Thus the prior dual damascene process has at least the below shortcomings:
(1) due to the use of two photolithography processes, two photo masks with different patterns must be used, thus complicating the process and increasing the cost.
(2) due to the two photolithography processes, misalignment or overlaying can easily occur.
Thus, a dual damascene process using a single photo mask is desired to solve the aforementioned problems.